Coated positive electrode materials for lithium ion batteries

ABSTRACT

High specific capacity lithium rich lithium metal oxide materials are coated with inorganic compositions, such as metal fluorides, to improve the performance of the materials as a positive electrode active material. The resulting coated material can exhibit an increased specific capacity, and the material can also exhibit improved cycling. The materials can be formed while maintaining a desired relatively high average voltage such that the materials are suitable for the formation of commercial batteries. Suitable processes are described for the synthesis of the desired coated compositions that can be adapted for commercial production.

CROSS REFERENCE TO RELATED APPLICATIONS

This patent application is a divisional of copending U.S. patentapplication Ser. No. 12/616,226 filed Nov. 11, 2009, to Lopez et al.,entitled “Coated Positive Electrode Materials for Lithium IonBatteries,” incorporated herein by reference.

FIELD OF THE INVENTION

The invention relates to coated positive electrode active materials forlithium ion batteries, and in particular lithium rich positive electrodeactive materials with an inert coating. The invention further relates tobatteries with improved performance properties as a result of selectedcoating of the positive electrode active materials.

BACKGROUND OF THE INVENTION

Lithium batteries are widely used in consumer electronics due to theirrelatively high energy density. Rechargeable batteries are also referredto as secondary batteries, and lithium ion secondary batteries generallyhave a negative electrode material that incorporates lithium when thebattery is charged. For some current commercial batteries, the negativeelectrode material can be graphite, and the positive electrode materialcan comprise lithium cobalt oxide (LiCoO₂). In practice, only a modestfraction of the theoretical capacity of the positive electrode activematerial generally can be used. At least two other lithium-basedpositive electrode active materials are also currently in commercialuse. These two materials are LiMn₂O₄, having a spinel structure, andLiFePO₄, having an olivine structure. These other materials have notprovided any significant improvements in energy density.

Lithium ion batteries are generally classified into two categories basedon their application. The first category involves high power battery,whereby lithium ion battery cells are designed to deliver high current(Amperes) for such applications as power tools and Hybrid ElectricVehicles (HEVs). However, by design, these battery cells are lower inenergy since a design providing for high current generally reduces totalenergy that can be delivered from the battery. The second designcategory involves high energy batteries, whereby lithium ion batterycells are designed to deliver low to moderate current (Amperes) for suchapplications as cellular phones, lap-top computers, Electric Vehicles(EVs) and Plug in Hybrid Electric Vehicles (PHEVs) with the delivery ofhigher total capacity.

SUMMARY OF THE INVENTION

In a first aspect, the invention pertains to a lithium ion batterypositive electrode material comprising an active composition representedby the formula Li_(1+x)M_(1−x)O₂, where M is a metal element or acombination thereof and 0.01≦x≦0.3, coated with an inorganic coatingcomposition wherein the coating composition comprises a metal/metalloidfluoride.

In a further aspect, the invention pertains to a lithium ion batterycomprising a positive electrode, a negative electrode comprising alithium incorporation composition, a separator between the positiveelectrode and the negative electrode and an electrolyte comprisinglithium ions. Generally, the positive electrode comprises an activematerial, distinct electrically conductive powders and a polymer binder,wherein the positive electrode active material comprises an activecomposition coated with an inorganic coating composition. The positiveelectrode active material can have a discharge specific capacity of atleast about 190 mAh/g with a discharge rate of 2 C from 4.6 volts to 2.0volts at room temperature for the fifteenth charge/discharge cycle. Insome embodiments, the active composition can be approximatelyrepresented by the formula Li_(1+x)Mi_(1−x)O₂, where M is a metalelement or a combination thereof and 0.01≦x≦0.3, coated with aninorganic coating composition.

In another aspect, the invention pertains to a lithium ion batterycomprising a positive electrode, a negative electrode comprising alithium incorporation composition and a separator between the positiveelectrode and the negative electrode, in which the positive electrodecomprises an active material having an active composition coated with aninorganic composition, distinct electrically conductive powers and apolymer binder. The positive electrode active material can have adischarge specific capacity of at least about 245 mAh/g, an averagevoltage of at least about 3.55 volts and a capacity at 40 cycles that isat least about 90% of the capacity at 10 cycles with a discharge rate ofC/3 from 4.6 volts to 2.0 volts at room temperature.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic drawing of a battery structure separated from acontainer.

FIG. 2A is a SEM micrograph of uncoated high capacity cathode lithiumoxide material at 100 micron resolution relative to a reference bar asshown in the distance scale legend.

FIG. 2B is an SEM micrograph of uncoated high capacity cathode lithiumoxide material at 20 micron resolution relative to a reference bar asshown in the distance scale legend.

FIG. 2C is an SEM micrograph of AlF₃ coated high capacity cathodelithium metal oxide material at (c) 100 micron resolution relative to areference bar as shown in the distance scale legend.

FIG. 2D is an SEM micrograph of AlF₃ coated high capacity cathodelithium metal oxide material at 20 micron resolution relative to areference bar as shown in the distance scale legend.

FIG. 3 is a plot of an X-ray diffraction spectrum of uncoated (pristine)high capacity cathode lithium metal oxide material sample and samplescoated with varying thickness of AlF₃.

FIG. 4A is a plot of cell voltage versus specific capacities of auncoated high specific capacity cathode lithium metal oxide materialcycled in the voltage range of 2.0 V-4.6 V at a charge/discharge rate of0.1 C for the 1st cycle.

FIG. 4B is a plot of cell voltage versus specific capacities of auncoated high specific capacity cathode lithium metal oxide materialcycled in the voltage range of 2.0 V-4.6 V at a charge/discharge rate of1/3 C for the seventh cycle.

FIG. 5 is a plot of specific discharge capacity versus cycle number ofan uncoated high capacity cathode lithium metal oxide material cycled at0.1 C for the first three cycles, 0.2 C for cycle numbers 4-6 and 0.33 Cfor cycle numbers 7-40.

FIG. 6A is a TEM micrograph of uncoated coated high specific capacitycathode lithium metal oxide materials.

FIG. 6B is a TEM micrograph of 7 nm AlF₃ coated high specific capacitycathode lithium metal oxide materials.

FIG. 6C is a TEM micrograph of 25 nm AlF₃ coated high specific capacitycathode lithium metal oxide materials.

FIG. 7 is a plot of differential scanning calorimetry data for uncoatedand four coated samples for the high capacity positive electrode activematerials.

FIG. 8 is a plot of electrochemistry impedance spectroscopy results forelectrodes formed with the positive electrode active materials for 5coated material samples.

FIG. 9A is a plot of cell voltage versus specific discharge capacitiesof a 3 nm AlF₃ coated high capacity cathode lithium metal oxide materialcycled in the voltage range of 2.0 V-4.6 V at a charge/discharge rate of0.1 C for the first cycle.

FIG. 9B is a plot of cell voltage versus specific discharge capacitiesof a 3 nm AlF₃ coated high capacity cathode lithium metal oxide materialcycled in the voltage range of 2.0 V-4.6 V at a charge/discharge rate of1/3 C for the 7th cycle.

FIG. 10 is a plot of specific discharge capacity versus cycle number ofa 3 nm AlF₃ coated high specific capacity cathode lithium metal oxidematerial cycled at 0.1 C for the first three cycles, 0.2 C for cyclenumbers 4-6 and 0.33 C for cycle numbers 7-40.

FIG. 11A is a set of two plots of cell voltage versus specific dischargecapacities of a 22 nm AlF₃ coated high specific capacity cathode lithiummetal oxide material cycled in the voltage range of 2.0 V-4.6 V at adischarge rate of 0.1 C for the 1st cycle.

FIG. 11B is a plot of cell voltage versus specific discharge capacitiesof a 22 nm AlF₃ coated high specific capacity cathode lithium metaloxide material cycled in the voltage range of 2.0 V-4.6 V at a dischargerate of 1/3 C for the 7th cycle.

FIG. 12 is a plot of specific discharge capacity versus cycle number ofa 22 nm AlF₃ coated high specific capacity cathode lithium metal oxidematerial cycled at 0.1 C for the first three cycles, 0.2 C for cyclenumbers 4-6 and 0.33 C for cycle number 7-40.

FIG. 13 is a set comparison plots of specific discharge capacity versuscycle number for a high specific capacity cathode lithium metal oxidematerial, uncoated and five different AlF₃ coating thicknesses, cycledat 0.1 C for the first three cycles, 0.2 C for cycle numbers 4-6 and0.33 C for cycle 7-40.

FIG. 14A is a plot of percentage irreversible capacity loss (IRCL)versus AlF₃ coating thickness of the high specific capacity cathodematerial.

FIG. 14B is a plot of specific IRCL versus AlF₃ coating thickness of thehigh specific capacity cathode material.

FIG. 15A is a plot of average voltage versus AlF₃ coating thickness ofthe high specific capacity cathode material.

FIG. 15B is a plot of percentage of average voltage reduction versusAlF₃ coating thickness of the high specific capacity cathode material.

FIG. 16 is a plot of coulombic efficiency between the first and 34^(th)cycles cycled at 0.33 C versus AlF₃ coating thickness of the highspecific capacity cathode material.

FIG. 17 is a plot of x-ray diffractograms for a lithium metal oxide withone of four different metal bifluoride coatings.

FIG. 18A is a transmission electron micrograph showing the coating forMgF₂ with an average thickness of about 3 nm.

FIG. 18B is a transmission electron micrograph showing the coating forSrF₂ with an average thickness of about 2 nm.

FIG. 19 is a plot of cell voltage versus specific capacity for the firstcharge and discharge cycle at a rate of C/10 for a battery formed withan uncoated high capacity positive electrode active material.

FIG. 20 is a plot of cell voltage versus specific capacity for the firstcharge and discharge cycle at a rate of C/10 for a battery formed with ahigh capacity positive electrode active material coated with MgF₂.

FIG. 21 is a plot of cell voltage versus specific capacity for the firstcharge and discharge cycle at a rate of C/10 for a battery formed with ahigh capacity positive electrode active material coated with SrF₂.

FIG. 22 is a plot of cell voltage versus specific capacity for the firstcharge and discharge cycle at a rate of C/10 for a battery formed with ahigh capacity positive electrode active material coated with BaF₂.

FIG. 23 is a plot of cell voltage versus specific capacity for the firstcharge and discharge cycle at a rate of C/10 for a battery formed with ahigh capacity positive electrode active material coated with CaF₂.

FIG. 24 is a plot of specific discharge capacity as a function of cyclenumber for five batteries respectively formed with uncoated positiveelectrode active materials or with positive electrode active materialscoated with MgF₂, SrF₂, B aF₂ or CaF₂.

FIG. 25 is a graph with plots of specific discharge capacity as afunction of cycle number for coin cell batteries formed with a negativeelectrode comprising graphite and a positive electrode having a highcapacity active material that is uncoated or coated with an indicatedaverage thickness of AlF₃.

FIG. 26A is a transmission electron micrograph showing AlF₃ coatings ona second lithium rich active material with an average thickness of about3 nm.

FIG. 26B is a transmission electron micrograph showing AlF₃ coatings ona second lithium rich active material with an average thickness of about17 nm.

FIG. 27 is a plot of cell voltage versus specific capacity for the firstcharge and discharge cycle at a rate of C/10 for a battery formed withan alternative positive electrode active material with cycling between2.0V and 4.3V.

FIG. 28 is a plot of cell voltage versus specific capacity for the firstcharge and discharge cycle at a rate of C/10 for a battery formed withthe alternative positive electrode active material having an AlF₃coating with cycling between 2.0V and 4.3V.

FIG. 29 is a plot of cell voltage versus specific capacity for the firstcharge and discharge cycle at a rate of C/10 for a battery formed withthe alternative positive electrode active material with cycling between2.0V and 4.5V.

FIG. 30 is a plot of cell voltage versus specific capacity for the firstcharge and discharge cycle at a rate of C/10 for a battery formed withthe alternative positive electrode active material having an AlF₃coating with cycling between 2.0V and 4.5V.

FIG. 31 is a set comparison plots of specific discharge capacity versuscycle number for the alternative positive active material, uncoated andfive different AlF₃ coating thicknesses cycled at 0.1 C for the firsttwo cycles and 0.33 C for cycle 3-18.

FIG. 32 is a set comparison plots of specific discharge capacity versuscycle number for the alternative positive electrode active material,uncoated and five different AlF₃ coating thicknesses cycled between 2.0Vand 4.5V at 0.1 C for the first two cycles and 0.33 C for cycle 3-18.

DETAILED DESCRIPTION OF THE INVENTION

It has been discovered that lithium rich metal oxides can be effectivelycoated at relatively small thicknesses with metalloid fluoride coatingsto significantly improve the performance of the resulting lithium ionbatteries. The lithium rich metal oxides are capable of being stablycharged to high voltages with resulting higher discharge capacitiesrelative to some lower voltage materials. The coatings can improve αrange of properties of the resulting batteries. In particular, thecoated materials can exhibit high average voltages that can provide amore consistent voltage over a wide range of the battery capacity. Thematerials can be synthesized effectively using techniques that arereadily scalable for commercial production. In addition, the materialscan be synthesized at high tap densities, such that the resultingbatteries can exhibit high effective capacities for a given batteryvolume. Furthermore, the batteries exhibit high specific capacities andexcellent cycling at moderate rate charging and discharging. Thin inertmetal oxide or metal phosphate coatings can also provide desiredperformance properties for resulting batteries formed with thematerials. Therefore, the materials can be effectively used forcommercial applications involving moderate discharge rate capability,such as plug in hybrid electric vehicles.

Lithium ion batteries described herein have achieved improved cyclingperformance while exhibiting high specific capacity and high overallcapacity. Suitable synthesis techniques for the lithium rich metaloxides include, for example, co-precipitation approaches or sol-gelsynthesis. Use of a metal fluoride coating, a metal oxide coating orother suitable coatings provides enhanced cycling performance. Thepositive electrode materials also exhibit a high average voltage over adischarge cycle so that the batteries have high power output along witha high specific capacity. The materials can also exhibit high specificcapacities at surprisingly high rates, such as 2 C discharge rates. As aresult of a relatively high tap density and excellent cyclingperformance, the battery exhibit continuing high capacity when cycled.Furthermore, the positive electrode materials demonstrate a reducedamount of irreversible capacity loss during the first charge anddischarge cycle of the battery so that negative electrode material canbe correspondingly reduced. The combination of excellent cyclingperformance, high specific capacity, and high overall capacity makethese resulting lithium ion batteries an improved power source,particularly for high energy applications, such as electric vehicles,plug in hybrid vehicles and the like.

The batteries described herein are lithium ion batteries in which anon-aqueous electrolyte solution comprises lithium ions. For secondarylithium ion batteries, lithium ions are released from the negativeelectrode during discharge such that the negative electrode functions asan anode during discharge with the generation of electrons from theoxidation of lithium upon its release from the electrode.Correspondingly, the positive electrode takes up lithium ions throughintercalation or a similar process during discharge such that thepositive electrode functions as a cathode which consumes electronsduring discharge. Upon recharging of the secondary battery, the flow oflithium ions is reversed through the battery with the negative electrodetaking up lithium and with the positive electrode releasing lithium aslithium ions. Generally, the batteries are formed with lithium ions inthe positive electrode material such that an initial charge of thebattery transfers a significant fraction of the lithium from thepositive electrode material to the negative electrode material toprepare the battery for discharge.

The word “element” is used herein in its conventional way as referringto a member of the periodic table in which the element has theappropriate oxidation state if the element is in a composition and inwhich the element is in its elemental form, M⁰, only when stated to bein an elemental form. Therefore, a metal element generally is only in ametallic state in its elemental form or a corresponding alloy of themetal's elemental form. In other words, a metal oxide or other metalcomposition, other than metal alloys, generally is not metallic.

In some embodiments, the lithium ion batteries can use a positiveelectrode active material that is lithium rich relative to a referencehomogenous electroactive lithium metal oxide composition. In someembodiments, the excess lithium can be referenced relative to acomposition LiMO₂, where M is one or more metals with an averageoxidation state of +3. The additional lithium in the initial cathodematerial provides corresponding additional lithium that can betransferred to the negative electrode during charging that can increasethe battery capacity for a given weight of cathode active material. Insome embodiments, the additional lithium is accessed at higher voltagessuch that the initial charge takes place at a higher voltage to accessthe additional capacity represented by the additional lithium of thepositive electrode.

It is believed that appropriately formed lithium-rich lithium metaloxides have a composite crystal structure in which the excess lithiumsupports the formation of an alternative crystalline phase. For example,in some embodiments of lithium rich materials, a Li₂MnO₃ material may bestructurally integrated with either a layered LiMnO₂ component orsimilar composite compositions with the manganese cations substitutedwith other transition metal cations with appropriate oxidation states.In some embodiments, the positive electrode material can be representedin two component notation as x Li₂M′O₃.(1−x)LiMO₂ where M is one or moremetal cations with an average valance of +3 with at least one cationbeing a Mn ion or a Ni ion and where M′ is one or more metal cationswith an average valance of +4. These compositions are described further,for example, in U.S. Pat. No. 6,680,143 to Thackeray et al., entitled“Lithium Metal Oxide Electrodes for Lithium Cells and Batteries,”incorporated herein by reference. Positive electrode active materials ofparticular interest have a formula Li_(1+x)Ni_(α)Mn_(β)Co_(γ)A₆₇ O₂,where x ranges from about 0.05 to about 0.3, α ranges from about 0.1 toabout 0.4, β range from about 0.3 to about 0.65, γ ranges from about 0to about 0.4, and δ ranges from about 0 to about 0.15, and where A isMg, Sr, Ba, Cd, Zn, Al, Ga, B, Zr, Ti, Ca, Ce, Y, Nb, Cr, Fe, V, Li orcombinations thereof.

Furthermore, surprisingly large capacities have been obtained forLi[Li_(0.2)Ni_(0.175)Co_(0.10)Mn_(0.525)]O₂, as presented in copendingU.S. patent application Ser. No. 12/332,735 to Lopez et al. (the '735application), now U.S. Pat. No. 8,465,873 B2, entitled “PositiveElectrode Material for High Specific Discharge Capacity Lithium IonBatteries”, incorporated herein by reference. The materials in the '735application were synthesized using a carbonate co-precipitation process.Also, very high specific capacities were obtained for this compositionusing hydroxide co-precipitation and sol gel synthesis approaches asdescribed in U.S. application Ser. No. 12/246,814 to Venkatachalam etal. (the '814 application), now U.S. Pat. No. 8,389,260 B2 entitled“Positive Electrode Material for Lithium Ion Batteries Having a HighSpecific Discharge Capacity and Processes for the Synthesis of theseMaterials”, incorporated herein by reference. These compositions have alow risk of fire for improved safety properties due to their specificcompositions with a layered structure and reduced amounts of nickelrelative to some other high capacity cathode materials. Thesecompositions use low amounts of elements that are less desirable from anenvironmental perspective, and can be produced from starting materialsthat have reasonable cost for commercial scale production. A carbonateco-precipitation process has been performed for the desired lithium richmetal oxide materials described herein having nickel, cobalt andmanganese cations in the composition and exhibiting the high specificcapacity performance. In addition to the high specific capacity, thematerials exhibit superior tap density which leads to high overallcapacity of the material in fixed volume applications. As demonstratedin the examples below, the lithium rich metal oxide materials formedwith the carbonate co-precipitation process have improved performanceproperties. Specifically, the specific lithium rich composition of theprevious paragraph formed by the carbonate co-precipitation process isused in coated forms to generate the results in the Examples below.

When the corresponding batteries with the intercalation-based positiveelectrode active materials are in use, the intercalation and release oflithium ions from the lattice induces changes in the crystalline latticeof the electroactive material. As long as these changes are essentiallyreversible, the capacity of the material does not change significantlywith cycling. However, the capacity of the active materials is observedto decrease with cycling to varying degrees. Thus, after a number ofcycles, the performance of the battery falls below acceptable values,and the battery is replaced. Also, on the first cycle of the battery,generally there is an irreversible capacity loss that is significantlygreater than per cycle capacity loss at subsequent cycles. Theirreversible capacity loss is the difference between the charge capacityof the new battery and the first discharge capacity. To compensate forthis first cycle irreversible capacity loss, extra electroactivematerial can be included in the negative electrode such that the batterycan be fully charged even though this lost capacity is not accessibleduring most of the life of the battery. Due to the inclusion ofadditional negative electrode active material to compensate for theirreversible capacity loss, negative electrode material is essentiallywasted. The irreversible capacity lose generally can be attributed tochanges during the initial charge-discharge cycle of the batterymaterials that are substantially maintained during subsequent cycling ofthe battery. Some of these irreversible capacity losses can beattributed to the positive electrode active materials, and the coatedmaterials described herein result in a decrease in the irreversiblecapacity loss of the batteries.

Appropriate coating materials can both improve the long term cyclingperformance of the material as well as decrease the first cycleirreversible capacity loss.

While not wanting to be limited by theory, the coatings may stabilizethe crystal lattice of the positive electrode active material during theuptake and release of lithium ions so that irreversible changes in thecrystal lattice are reduced significantly. In particular, metal fluoridecompositions can be used as effective coatings. The general use of metalfluoride compositions as coatings for cathode active materials,specifically LiCoO₂ and LiMn₂O₄, is described in published PCTapplication WO 2006/109930A to Sun et al., entitled “Cathode ActiveMaterial Coated with Fluorine Compound for Lithium Secondary Batteriesand Method for Preparing the Same,” incorporated herein by reference.

It has been discovered that metal fluoride coatings can providesignificant improvements for lithium rich layered positive electrodeactive materials. In particular, AlF₃ can be a desirable coatingmaterial due to reasonable cost of the materials and the relatively lowenvironmental concerns associated with aluminum ions, although othermetals fluorides also are suitable. The performance improvementsassociated with the coating materials can relate to long term cyclingwith significantly reduced degradation of capacity, a significantdecrease in first cycle irreversible capacity loss and an improvement inthe capacity generally. Since the coating materials are believed to beinactive in the cell cycling, it is surprising that the coatingmaterials can increase the active materials specific capacities. Theamount of coating material can be selected to accentuate the observedperformance improvements. The improvements lithium rich positiveelectrode active materials are described further in the '735 applicationand the '814 application.

The materials described herein also exhibit a large tap density. Ingeneral, when specific capacities are comparable, a larger tap densityof a positive electrode material results in a higher overall capacity ofa battery. The large tap density of the active material also can resultin a battery with a greater specific energy and specific power.Generally, a battery with a greater capacity can provide for longerdischarge times for a specific application. Thus, these batteries canexhibit a meaningfully improved performance. It is useful to note thatduring charge/discharge measurements, the specific capacity of amaterial depends on the rate of discharge. The greatest specificcapacity of a particular material is measured at very slow dischargerates. In actual use, the actual specific capacity is less than themaximum value due to discharge at a faster rate. More realistic specificcapacities can be measured using reasonable rates of discharge that aremore similar to the rates encountered during actual use. For low tomoderate rate applications, a reasonable testing rate involves adischarge of the battery over three hours. In conventional notation thisis written as C/3 or 0.33 C. Faster or slower discharge rates can beused as desired.

In general, the improvements in the battery performance properties donot all correlate with the same coating thickness. These properties arestudied in more detail below and corresponding results are presented inthe Examples. In summary, the decrease in irreversible capacity lossplateaus at roughly 10 nanometers(nm) of coating thickness. With respectto average voltage, the coating tends to decrease the average voltage,but the average voltage is not significantly decreased with thinnercoatings. With respect to the specific capacity, the specific capacityfirst increases and then decreases as the coating thickness increases.And the specific capacity results change with cycling and the rate ofthe discharge.

A set of results are presented in the Examples below that provideinformation useful for evaluating appropriate coating thicknesses fordesirable battery performance for high voltage batteries with reasonablelong term cycling properties. It is found that thicker metal fluoridecoatings with a thickness of roughly 20 nm or greater have a significantreduction in irreversible capacity loss. Materials with these thickcoatings also exhibit good cycling over 34 charge-discharge cycles at aC/3 rate. However, these materials exhibit a significant drop in theaverage voltage. These materials with thicker coatings also exhibitreduced specific capacities relative to thinner coatings. The drop inspecific capacity for the materials with the thicker coating is morepronounced at higher rates, which might suggest that thicker coatingsimpede the movement of lithium ions past the thicker coating.

At moderate metal fluoride coating thicknesses between about 8 nm andabout 20 nm, the materials exhibit most of the decrease with respect toirreversible capacity loss as observed with materials with greatercoating thicknesses. Furthermore, the average voltages are greater thanobtained with thicker coatings. In addition, the specific capacity ofthese materials is similarly greater than for the same activecomposition with a greater coating thickness. However, the positiveelectrode active materials with intermediate coating thicknesses canhave significantly poorer coulombic efficiency relative to materialswith a greater coating thickness. In other words, the specific capacityof the materials with the greater coating thickness fades more quicklywith cycling. Thus, if the results are extrapolated to a greater numberof cycles, the positive electrode active materials with intermediatethickness metal fluoride coatings would be expected to undesirably poorcycling properties in most applications.

Surprisingly, the positive electrode active materials with thinner metalfluoride coatings display surprisingly desirable results. Thus, positiveelectrode active materials with a metal fluoride coating having acoating thickness from about 0.5 nm to about 12 nm have desirable andsurprisingly good properties when incorporated into batteries. These,materials exhibit less of a decrease in irreversible capacity loss. Butirreversible capacity loss is not the most significant property of thematerials in the context of longer term cycling. The positive electrodeactive materials with a thinner metal fluoride coating have a greateraverage voltage, which can be comparable to the average voltage of theuncoated material. These materials can have high initial specificcapacities, and the materials can exhibit a desirable coulombicefficiency such that the fade with cycling is low at moderate rates outto at least 40 cycles.

Rechargeable batteries have α range of uses, such as mobilecommunication devices, such as phones, mobile entertainment devices,such as MP3 players and televisions, portable computers, combinations ofthese devices that are finding wide use, as well as transportationdevices, such as automobiles and fork lifts. Most of the batteries usedin these electronic devices have a fixed volume. It is therefore highlydesirable that the positive electrode material used in these batterieshas a high tap density so there is essentially more chargeable materialin the positive electrode yielding a higher total capacity of thebattery. The batteries described herein that incorporate improvedpositive electrode active materials with respect to specific capacity,tap density, and cycling can provide improved performance for consumers,especially for medium current applications.

The batteries described herein are suitable for vehicle applications. Inparticular, these batteries can be used in battery packs for hybridvehicles, plug-in hybrid vehicles and purely electric vehicles. Thesevehicles generally have a battery pack that is selected to balanceweight, volume and capacity. While larger battery packs can provide agreater range on electric operation, larger packs take up more room thatis then not available for other purposes and have greater weight thatcan decrease performance. Thus, due to the high capacity of thebatteries described herein, a battery pack that yields a desired amountof total power can be made in a reasonable volume, and these batterypacks can correspondingly achieve the excellent cycling performancedescribed herein.

Battery Structure

Referring to FIG. 1, a battery 100 is shown schematically having anegative electrode 102, a positive electrode 104 and a separator 106between negative electrode 102 and positive electrode 104. A battery cancomprise multiple positive electrodes and multiple negative electrodes,such as in a stack, with appropriately placed separators. Electrolyte incontact with the electrodes provides ionic conductivity through theseparator between electrodes of opposite polarity. A battery generallycomprises current collectors 108, 110 associated respectively withnegative electrode 102 and positive electrode 104.

Lithium has been used in both primary and secondary batteries. Anattractive feature of lithium metal is its light weight and the factthat it is the most electropositive metal, and aspects of these featurescan be advantageously captured in lithium ion batteries also. Certainforms of metals, metal oxides, and carbon materials are known toincorporate lithium ions into the structure through intercalation,alloying or similar mechanisms. Desirable mixed metal oxides aredescribed further herein to function as electroactive materials forpositive electrodes in secondary lithium ion batteries. Lithium ionbatteries refer to batteries in which the negative electrode activematerial is a material that takes up lithium during charging andreleases lithium during discharging. If lithium metal itself is used asthe anode, the resulting battery generally is simply referred to as alithium battery.

The nature of the negative electrode intercalation material influencesthe resulting voltage of the battery since the voltage is the differencebetween the half cell potentials at the cathode and anode. Suitablenegative electrode lithium intercalation compositions can include, forexample, graphite, synthetic graphite, coke, fullerenes, niobiumpentoxide, tin alloys, silicon, titanium oxide, tin oxide, and lithiumtitanium oxide, such as Li_(x)TiO₂, 0.5<x≦1 or Li_(1+x)Ti_(2−x)O₄,0≦x≦1/3. Additional negative electrode materials are described incopending patent applications Ser. No. 12/502,609, now U.S. Pat. No.9,012,073 B2 to Kumar, entitled “Composite Compositions, NegativeElectrodes with Composite Compositions and Corresponding Batteries,” andSer. No. 12/429,438, now issued U.S. Pat. No. 8,277,974 to Kumar et al.,entitled “Lithium Ion Batteries with Particular Negative ElectrodeCompositions,” both of which are incorporated herein by reference.

The positive electrode active compositions and negative electrode activecompositions generally are powder compositions that are held together inthe corresponding electrode with a polymer binder. The binder providesionic conductivity to the active particles when in contact with theelectrolyte. Suitable polymer binders include, for example,polyvinylidine fluoride, polyethylene oxide, polyethylene,polypropylene, polytetrafluoroethylene, polyacrylates, rubbers, e.g.ethylene-propylene-diene monomer (EPDM) rubber or styrene butadienerubber (SBR), copolymers thereof, or mixtures thereof. The particleloading in the binder can be large, such as greater than about 80 weightpercent. To form the electrode, the powders can be blended with thepolymer in a suitable liquid, such as a solvent for the polymer. Theresulting paste can be pressed into the electrode structure. In someembodiments, the batteries can be constructed based on the methoddescribed in copending patent application Ser. No. 12/403,521, now U.S.Pat. No. 8,187,752 to Buckley et al, entitled “High Energy Lithium IonSecondary Batteries”, incorporated herein by reference.

The positive electrode composition, and possibly the negative electrodecomposition, generally also comprises an electrically conductive powderdistinct from the electroactive composition. Suitable supplementalelectrically conductive powders include, for example, graphite, carbonblack, metal powders, such as silver powders, metal fibers, such asstainless steel fibers, and the like, and combinations thereof.Generally, a positive electrode can comprise from about 1 weight percentto about 25 weight percent, and in further embodiments from about 2weight percent to about 15 weight percent distinct electricallyconductive powder. A person of ordinary skill in the art will recognizethat additional ranges of amounts of electrically conductive powderswithin the explicit ranges above are contemplated and are within thepresent disclosure.

The electrode generally is associated with an electrically conductivecurrent collector to facilitate the flow of electrons between theelectrode and an exterior circuit. The current collector can comprisemetal, such as a metal foil or a metal grid. In some embodiments, thecurrent collector can be formed from nickel, aluminum, stainless steel,copper or the like. The electrode material can be cast as a thin filmonto the current collector. The electrode material with the currentcollector can then be dried, for example in an oven, to remove solventfrom the electrode. In some embodiments, the dried electrode material incontact with the current collector foil or other structure can besubjected to a pressure from about 2 to about 10 kg/cm² (kilograms persquare centimeter).

The separator is located between the positive electrode and the negativeelectrode. The separator is electrically insulating while providing forat least selected ion conduction between the two electrodes. A varietyof materials can be used as separators.

Commercial separator materials are generally formed from polymers, suchas polyethylene and/or polypropylene that are porous sheets that providefor ionic conduction. Commercial polymer separators include, forexample, the Celgard® line of separator material from Hoechst Celanese,Charlotte, N.C. Also, ceramic-polymer composite materials have beendeveloped for separator applications. These composite separators can bestable at higher temperatures, and the composite materials cansignificantly reduce the fire risk. The polymer-ceramic composites forseparator materials are described further in U.S. patent application2005/0031942A to Hennige et al., entitled “Electric Separator, Methodfor Producing the Same and the Use Thereof,” incorporated herein byreference. Polymer-ceramic composites for lithium ion battery separatorsare sold under the trademark Separion® by Evonik Industries, Germany.

We refer to solutions comprising solvated ions as electrolytes, andionic compositions that dissolve to form solvated ions in appropriateliquids are referred to as electrolyte salts. Electrolytes for lithiumion batteries can comprise one or more selected lithium salts.Appropriate lithium salts generally have inert anions. Suitable lithiumsalts include, for example, lithium hexafluorophosphate, lithiumhexafluoroarsenate, lithium bis(trifluoromethyl sulfonyl imide), lithiumtrifluoromethane sulfonate, lithium tris(trifluoromethyl sulfonyl)methide, lithium tetrafluoroborate, lithium perchlorate, lithiumtetrachloroaluminate, lithium chloride, lithium difluoro oxalato borate,and combinations thereof. Traditionally, the electrolyte comprises a 1 Mconcentration of the lithium salts, although greater or lesserconcentrations can be used.

For lithium ion batteries of interest, a non-aqueous liquid is generallyused to dissolve the lithium salt(s). The solvent generally does notdissolve the electroactive materials. Appropriate solvents include, forexample, propylene carbonate, dimethyl carbonate, diethyl carbonate,2-methyl tetrahydrofuran, dioxolane, tetrahydrofuran, methyl ethylcarbonate, γ-butyrolactone, dimethyl sulfoxide, acetonitrile, formamide,dimethyl formamide, triglyme (tri(ethylene glycol) dimethyl ether),diglyme (diethylene glycol dimethyl ether), DME (glyme or1,2-dimethyloxyethane or ethylene glycol dimethyl ether), nitromethaneand mixtures thereof.

The electrodes described herein can be incorporated into variouscommercial battery designs. For example, the cathode compositions can beused for prismatic shaped batteries, wound cylindrical batteries, coinbatteries or other reasonable battery shapes. The testing in theExamples is performed using coin cell batteries. The batteries cancomprise a single cathode structure or a plurality of cathode structuresassembled in parallel and/or series electrical connection(s). While thepositive electrode active materials can be used in batteries forprimary, or single charge use, the resulting batteries generally havedesirable cycling properties for secondary battery use over multiplecycling of the batteries.

In some embodiments, the positive electrode and negative electrode canbe stacked with the separator between them, and the resulting stackedstructure can be rolled into a cylindrical or prismatic configuration toform the battery structure. Appropriate electrically conductive tabs canbe welded or the like to the current collectors, and the resultingjellyroll structure can be placed into a metal canister or polymerpackage, with the negative tab and positive tab welded to appropriateexternal contacts. Electrolyte is added to the canister, and thecanister is sealed to complete the battery. Some presently usedrechargeable commercial batteries include, for example, the cylindrical18650 batteries (18 mm in diameter and 65 mm long) and 26700 batteries(26 mm in diameter and 70 mm long), although other battery sizes can beused.

Positive Electrode Active Materials

The positive electrode active materials comprise lithium intercalatingmetal oxide compositions. In some embodiments, the lithium metal oxidecompositions can comprise lithium rich compositions relative to areference composition. Generally, LiMO₂ can be considered the referencecomposition, and the lithium rich compositions can be referred to withan approximate formula Li_(1+x)M_(1−y)O₂, where M represents one or moremetals and y is related to x based on the average valance of the metals.In some embodiments, the lithium rich compositions generally arebelieved to form a layered composite crystal structure, and for theseembodiments x is approximately equal to y. In some embodiments, thecompositions comprise Ni, Co and Mn ions optionally along with one ormore additional metal ion dopants. It has been surprising found that thedopant improves the performance of the resulting compositions withrespect to the capacity after cycling. Furthermore, for coated samples,the average voltage can be increased with doping and some decrease inthe irreversible capacity loss has also been found. The desiredelectrode active materials can be synthesized using synthesis approachesdescribed herein.

The lithium rich compositions Li_(1+x)M_(1−y)O₂ provide additionallithium which can be available to contribute to the battery capacity.With the extra lithium loaded into the negative electrode duringcharging, these batteries can operate at higher voltages. Thus, thesematerials provide a desirable high voltage material with higher specificcapacities.

In some compositions of particular interest, the compositions can bedescribed by the formula Li_(1+x)Ni_(α)Mn_(β)Co_(γ)A_(δ)O₂m where xranges from about 0.01 to about 0.3, α ranges from about 0.1 to about0.4, β ranges from about 0.3 to about 0.65, γ ranges from about 0 toabout 0.4, δ ranges from about 0 (or 0.001 if not zero) to about 0.15,and where A is Mg, Sr, Ba, Cd, Zn, Al, Ga, B, Zr, Ti, Ca, Ce, Y, Nb, Cr,Fe, V, Li or combinations thereof. In some embodiments, the sumx+α+β+γ+δ of the positive electrode active material approximately equals1.0. A, which is in small amounts, can be considered a dopant element. Aperson of ordinary skill in the art will recognize that additionalranges of parameter values within the explicit ranges above arecontemplated and are within the present disclosure. Coatings for thesematerials are described further below.

With respect to some embodiments of materials described herein, Thackeryand coworkers have proposed a composite crystal structure for somelithium rich metal oxide compositions in which a Li₂M′O₃ composition isstructurally integrated into a layered structure with a LiMO₂ component.The electrode materials can be represented in two component notation asb Li₂M′O₃.(1−b) LiMO₂, where M is one or more metal elements with anaverage valance of +3 and with at least one element being Mn or Ni andM′ is a metal element with an average valance of +4 and 0<b<1, and insome embodiments 0.03≦b≦0.9. For example, M can be a combination ofNi⁺², Co⁺³ and Mn⁺⁴. The overall formula for these compositions can bewritten as Li_(1+b/(2+b))M′_(2b(2+b))M_(2(1−b)/(2+b))O₂. This formula isconsistent with the sum x+α+β+γ+δ equal to 1 in the formula of theprevious paragraph where x=b/(2+b). Batteries formed from thesematerials have been observed to cycle at higher voltages and with highercapacities relative to batteries formed with corresponding LiMO₂compositions. These materials are described generally in U.S. Pat. No.6,680,143 to Thackery et al., entitled Lithium Metal Oxide Electrodesfor Lithium

Cells and Batteries,” and U.S. Pat. No. 6,677,082 to Thackery et al.,entitled “Lithium Metal Oxide Electrodes for Lithium Cells andBatteries,” both of which are incorporated herein by reference. Thackeryidentified Mn, Ti and Zr as being of particular interest as M′ and Mnand Ni for M.

The structure of some specific layered structures is described furtherin Thackery et al., “Comments on the structural complexity oflithium-rich Li_(1+x)M_(1−x)O₂ electrodes (M=Mn,Ni,Co) for lithiumbatteries,” Electrochemistry Communications 8 (2006), 1531-1538,incorporated herein by reference. The study reported in this articlereviewed compositions with the formulasLi_(1+x)[Mn_(0.5)Ni_(0.5)]_(1−x)O₂ andLi_(−x)[Mn_(0.333)Ni_(0.333)Co_(0.333)]_(1−x)O₂. The article alsodescribes the structural complexity of the layered materials.

Recently, Kang and coworkers described a composition for use insecondary batteries with the formulaLi_(1+x)Ni_(α)Mn_(β)Co_(γ)M′_(δ)O_(2−z)F_(z), M′=Mg, Zn, Al, Ga, B, Zr,Ti, x between about 0 and 0.3, α between about 0.2 and 0.6, β betweenabout 0.2 and 0.6, γ between about 0 and 0.3, δ between about 0 and 0.15and z between about 0 and 0.2. The metal ranges and fluorine wereproposed as improving battery capacity and stability of the resultinglayered structure during electrochemical cycling. See U.S. Pat. No.7,205,072, to Kang et al. (the '072 patent), entitled “Layered cathodematerials for lithium ion rechargeable batteries,” incorporated hereinby reference. This reference reported a cathode material with a capacitybelow 250 mAh/g (milli-ampere hours per gram) at room temperature after10 cycles, which is at an unspecified rate that can be assumed to be lowto increase the performance value. Kang et al. examined various specificcompositions including Li_(1.2)Ni_(0.15)Mn_(0.55)Co_(0.10)O₂, which issimilar to the composition examined in the examples below.

The results obtained in the '072 patent involved a solid state synthesisof the materials that did not achieve comparable cycling capacity of thebatteries formed with cathode active materials formed withco-precipitation methods. The improved performance of the materialsformed by co-precipitation is described further in the '814 applicationand '735 application noted above. The co-precipitation process for thedoped materials described herein is described further below.

The performance of the positive electrode active materials is influencedby many factors. It has been found that a thin metal fluoride coating orother inorganic coating can notably improve many significant performanceparameters. Also, the mean particle size and the particle sizedistribution are two of the basic properties characterizing the positiveelectrode active materials, and these properties influence the ratecapabilities and tap densities of the materials. Because batteries havefixed volumes, it is therefore desirable that the material used in thepositive electrode of these batteries has a high tap density if thespecific capacity of the material can be maintained at a desirably highvalue. Then, the total capacity of the battery can be higher due to thepresence of more chargeable material in the positive electrode. Thecoatings can be added while still obtaining good tap densities using theprocesses to form the materials described herein. In general, tapdensities can be obtained of at least about 1.3 grams/milliliter (g/mL),in further embodiments at least about 1.6 g/mL and in some embodimentsat least about 2.0 g/mL, where the tap density can be obtained usingcommercial tapping apparatuses using reasonable tapping parameters. Aperson of ordinary skill in the art will recognize that additionalranges of tap density within the specific ranges above are contemplatedand are within the present disclosure.

Synthesis Methods

Synthesis approaches described herein can be used to form lithium richcathode active materials with improved specific capacity upon cyclingand a high tap density. The synthesis methods have been adapted for thesynthesis of compositions with the formulaLi_(1+x)Ni_(α)Mn_(β)Co_(γ)A_(δ)O₂, where x ranges from about 0.01 toabout 0.3, α ranges from about 0.1 to about 0.4, β ranges from about 0.3to about 0.65, γ ranges from about 0 to about 0.4, δ ranges from about 0to about 0.1, and where A is Mg, Sr, Ba, Cd, Zn, Al, Ga, B, Zr, Ti, Ca,Ce, Y, Nb, Cr, Fe, V, Li or combinations thereof. In some embodiments,the sum x+α+β+γ+δ of the positive electrode active materialapproximately equals 1.0, and for these embodiments, a layeredcrystalline structure can form as described above. The synthesisapproaches are also suitable for commercial scale up. Specifically,co-precipitation process can be used to synthesize the desired lithiumrich positive electrode materials with desirable results. Additionally,a solution assisted precipitation method discussed in detail below canbe used to coat the material with metal fluoride.

In the co-precipitation process, metal salts are dissolved into anaqueous solvent, such as purified water, with a desired molar ratio.Suitable metal salts include, for example, metal acetates, metalsulfates, metal nitrates, and combination thereof. The concentration ofthe solution is generally selected between 1M and 3M. The relative molarquantities of metal salts can be selected based on the desired formulafor the product materials. Similarly, the dopant elements can beintroduced along with the other metal salts at the appropriate molarquantity such that the dopant is incorporated into the precipitatedmaterial. The pH of the solution can then be adjusted, such as with theaddition of Na₂CO₃ and/or ammonium hydroxide, to precipitate a metalhydroxide or carbonate with the desired amounts of metal elements.Generally, the pH can be adjusted to a value between about 6.0 to about9.0. The solution can be heated and stirred to facilitate theprecipitation of the hydroxide or carbonate. The precipitated metalhydroxide or carbonate can then be separated from the solution, washedand dried to form a powder prior to further processing. For example,drying can be performed in an oven at about 110° C. for about 4 to about12 hours. A person of ordinary skill in the art will recognize thatadditional ranges of process parameters within the explicit ranges aboveare contemplated and are within the present disclosure.

The collected metal hydroxide or carbonate powder can then be subjectedto a heat treatment to convert the hydroxide or carbonate composition tothe corresponding oxide composition with the elimination of water orcarbon dioxide. Generally, the heat treatment can be performed in anoven, furnace or the like. The heat treatment can be performed in aninert atmosphere or an atmosphere with oxygen present. In someembodiments, the material can be heated to a temperature of at leastabout 350° C. and in some embodiments from about 400° C. to about 800°C. to convert the hydroxide or carbonate to an oxide. The heat treatmentgenerally can be performed for at least about 15 minutes, in furtherembodiments from about 30 minutes to 24 hours or longer, and inadditional embodiments from about 45 minutes to about 15 hours. Afurther heat treatment can be performed to improve the crystallinity ofthe product material. This calcination step for forming the crystallineproduct generally is performed at temperatures of at least about 650°C., and in some embodiments from about 700° C. to about 1200° C., and infurther embodiments from about 700° C. to about 1100° C. The calcinationstep to improve the structural properties of the powder generally can beperformed for at least about 15 minutes, in further embodiments fromabout 20 minutes to about 30 hours or longer, and in other embodimentsfrom about 1 hour to about 36 hours. The heating steps can be combined,if desired, with appropriate ramping of the temperature to yield desiredmaterials. A person of ordinary skill in the art will recognize thatadditional ranges of temperatures and times within the explicit rangesabove are contemplated and are within the present disclosure.

The lithium element can be incorporated into the material at one or moreselected steps in the process. For example, a lithium salt can beincorporated into the solution prior to or upon performing theprecipitation step through the addition of a hydrated lithium salt. Inthis approach, the lithium species is incorporated into the hydroxide orcarbonate material in the same way as the other metals. Also, due to theproperties of lithium, the lithium element can be incorporated into thematerial in a solid state reaction without adversely affecting theresulting properties of the product composition. Thus, for example, anappropriate amount of lithium source generally as a powder, such asLiOH.H₂O, LiOH, Li₂CO_(3,) or a combination thereof, can be mixed withthe precipitated metal carbonate or metal hydroxide. The powder mixtureis then advanced through the heating step(s) to form the oxide and thenthe crystalline final product material.

Further details of the hydroxide co-precipitation process are describedin the '814 application referenced above. Further details of thecarbonate co-precipitation process are described in the '735 applicationreferenced above.

Coatings and Methods for Forming the Coatings

Inert inorganic coatings, such as metal fluoride coatings, have beenfound to significantly improve the performance of the lithium richlayered positive electrode active materials described herein. However,there are tradeoffs with respect to the resulting battery properties asa function of the coating thickness. As described herein the effects ofthe coating on battery performance is evaluated for a matrix ofsignificant battery performance parameters. The evaluation ofperformance with the coating thickness yields relatively complexrelationships. It has been surprisingly found that overall the bestperformance improvements results from thin coatings, no more than about8 nm thick. The improvement in battery properties is described in detailin the following section.

The coating can provide improvements in the performance of the highcapacity lithium rich compositions described herein in lithium ionsecondary batteries. In general, a selected metal fluoride or metalloidfluoride can be used for the coating. Similarly, a fluoride coating witha combination of metal and/or metalloid elements can be used.Metal/metalloid fluoride coatings have been proposed to stabilize theperformance of positive electrode active materials for lithium secondarybatteries. Suitable metals and metalloid elements for the fluoridecoatings include, for example, Al, Bi, Ga, Ge, In, Mg, Pb, Si, Sn, Ti,Tl, Zn, Zr and combinations thereof. Aluminum fluoride can be adesirable coating material since it has a reasonable cost and isconsidered environmentally benign. The metal fluoride coating aredescribed generally in published PCT application WO 2006/109930A to Sunet al., entitled “Cathode Active Materials Coated with Fluorine Compoundfor Lithium Secondary Batteries and Method for Preparing the Same,”incorporated herein by reference. This published patent applicationprovides results for LiCoO₂ coated with LiF, ZnF₂ or AlF₃. The Sun PCTapplication referenced above specifically refers to the followingfluoride compositions, CsF, KF, LiF, NaF, RbF, TiF, AgF, AgF₂, BaF₂,CaF₂, CuF₂, CdF₂, FeF₂, HgF₂, Hg₂F₂, MnF₂, MgF₂, NiF₂, PbF₂, SnF₂, SrF₂,XeF₂, ZnF₂, AlF_(3,) BF₃, BiF₃, CeF₃, CrF₃, DyF₃, EuF₃, GaF₃, GdF₃,FeF₃, HoF₃, InF₃, LaF₃, LuF₃, MnF₃, NdF₃, VOF₃, PrF₃, SbF₃, ScF₃, SmF₃,TbF₃, TiF₃, TmF₃, YF₃, YbF₃, TlF₃, CeF₄, GeF₄, HfF₄, SiF₄, SnF₄, TiF₄,VF₄, ZrF₄, NbF₅, SbF₅, TaF₅, BiF₅, MoF₆, ReF₆, SF₆, and WF₆.

The effect of an AlF₃ coating on the cycling performance ofLiNi_(1/3)Co_(1/3)Mn_(1/3)O₂ is described further in an article to Sunet al., “AlF₃-Coating to Improve High Voltage Cycling Performance ofLi[Ni_(1/3)Co_(1/3)Mn_(1/3)[O₂ Cathode Materials for Lithium SecondaryBatteries,” J. of the Electrochemical Society, 154 (3), A168-A172(2007). Also, the effect of an AlF₃ coating on the cycling performanceof LiNi_(0.8)Co_(0.1)Mn_(0.1)O₂ is described further in an article toWoo et al., “Significant Improvement of Electrochemical Performance ofAlF₃-Coated Li[Ni_(0.8)Co_(0.1)Mn_(0.1)]O₂ Cathode Materials,” J. of theElectrochemical Society, 154 (11) A1005-A1009 (2007), incorporatedherein by reference. An increase in capacity and a reduction inirreversible capacity loss were noted with Al₂O₃ coatings by Wu et al.,“High Capacity, Surface-Modified LayeredLi[Li_((1−x)/3)Mn_((2−x)/3)Co_(x/3)]O₂ Cathodes with Low IrreversibleCapacity Loss,” Electrochemical and Solid State Letters, 9 (5) A221-A224(2006), incorporated herein by reference. Improved metal oxide coatingsare described in copending U.S. provisional patent application Ser. No.61/253,286 to Venkatachalam et al., entitled “Metal Oxide CoatedPositive Electrode Materials for Lithium Ion Batteries,” incorporatedherein by reference. The use of a LiNiPO₄ coating to obtain improvedcycling performance is described in an article to Kang et al. “Enhancingthe rate capability of high capacity xLi₂MnO₃ (1−x)LiMO₂ (M=Mn, Ni, Co)electrodes by Li—Ni—PO₄ treatment,” Electrochemistry Communications 11,748-751 (2009), incorporated herein by reference.

It has been found that metal/metalloid fluoride coatings cansignificantly improve the performance of lithium rich layeredcompositions for lithium ion secondary batteries. See, for example, the'814 application and the '735 application cited above. In particular,the coating can improve the capacity of the batteries. However, thecoating itself is not electrochemically active. When the loss ofspecific capacity due to the amount of coating added to a sample exceedswhere the benefit of adding coating is offset by its electrochemicalinactivity, reduction in battery capacity can be expected. In general,the amount of coating can be selected to balance the beneficialstabilization resulting from the coating with the loss of specificcapacity due to the weight of the coating material that generally doesnot contribute directly to a high specific capacity of the material.

However, the battery properties as a function of coating thickness havebeen found to be complex. In particular, the coatings also influenceother properties of the active material, such as the average voltage,irreversible capacity loss, coulombic efficiency and impedance. Theselection of a desired coating thickness can be based on an evaluationof the overall range of battery properties that are observed forparticular coating thicknesses. In general, the coating can have athickness from about 0.05 nm to about 50 nm. However, as describedfurther below, it has been surprisingly found that thinner coatings canprovide the best overall performance parameters for secondary lithiumion batteries that are cycled extensively. In some embodiments ofparticular interest, the coatings have an average thickness form about0.5 nm to about 12 nm, in other embodiments from about 1 nm to about 10nm, in further embodiments from 1.25 nm to about 9 nm and in additionalembodiments from about 1.5 nm to about 8 nm. A person of ordinary skillin the art will recognize that additional ranges of coating materialwithin the explicit ranges above are contemplated and are within thepresent disclosure. The amount of AlF₃ effective in AlF₃ coated metaloxide materials to improve the capacity of the uncoated material isrelated to the particle size and surface area of the uncoated material.In general, the amount of coating material ranges from about 0.01 molepercent to about 10 mole percent, in further embodiments from about 0.05mole percent to about 7 mole percent, in additional embodiments fromabout 0.1 mole percent to about 5 mole percent, and in other embodimentsfrom about 0.2 mole percent to about 4 mole percent relative to thetotal metal content of the particles. A person of ordinary skill in theart will recognize that additional ranges of coating material within theexplicit ranges above are contemplated and are within the presentdisclosure.

The fluoride coating can be deposited using a solution basedprecipitation approach. A powder of the positive electrode material canbe mixed in a suitable solvent, such as an aqueous solvent. A solublecomposition of the desired metal/metalloid can be dissolved in thesolvent. Then, NH₄F can be gradually added to the dispersion/solution toprecipitate the metal fluoride. The total amount of coating reactantscan be selected to form the desired amount of coating, and the ratio ofcoating reactants can be based on the stoichiometry of the coatingmaterial. In particular, the desired thickness of coating can be formedthrough the addition of an appropriate amount of coating reactants. Theselection of the amount of coating material can be verified through anexamination of the product particles using electron microscopy asdescribed below in the Examples. The coating mixture can be heatedduring the coating process to reasonable temperatures, such as in therange from about 60° C. to about 100° C. for aqueous solutions for fromabout 20 minutes to about 48 hours, to facilitate the coating process.After removing the coated electroactive material from the solution, thematerial can be dried and heated to temperatures generally from about250° C. to about 600° C. for about 20 minutes to about 48 hours tocomplete the formation of the coated material. The heating can beperformed under a nitrogen atmosphere or other substantially oxygen freeatmosphere. Specific procedures for the formation of AlF₃, MgF₂, CaF₂,SrF₂ and BaF₂ coatings are described in the examples below. Theformation of inert metal oxide coatings, such as A1202, and Li—Ni—PO₄coatings are described in the articles cited above.

Battery Performance

Batteries formed from the coated positive electrode active materialsdescribed herein have demonstrated superior performance under realisticdischarge conditions for moderate current applications. Specifically,the active materials have demonstrated a high specific capacity uponcycling of the batteries at moderate discharge rates. Furthermore, somecoated positive electrode active materials have demonstrated improvedcycling out to a large number of cycles. It has surprisingly been foundthat a thinner coating provides an overall more desirable performanceprofile than batteries formed with positive electrode active materialswith a thicker coating. In particular, thinner coatings have improvedcycling and a greater average discharge voltage. While active materialswith thinner coatings result in batteries with less of a decrease inirreversible capacity loss, the thin coatings can be used to formbatteries with some decrease in irreversible capacity loss, and theother improved properties of the batteries formed with the materialswith the thinner coatings are more significant than the differences withrespect to the irreversible capacity loss. Thus, coatings having anaverage thickness from about 0.5 to about 8 nm have been found inparticular to provide the desired balance to obtain excellentperformance characteristics.

As noted above, the irreversible capacity loss is the difference betweenthe first charge specific capacity and the first discharge specificcapacity. With respect to the values described herein, the irreversiblecapacity loss is in the context of the positive electrode activematerials, which is evaluated relative to a lithium metal negativeelectrode. It is desirable to reduce the irreversible capacity loss sothat additional negative electrode active material is not needed tobalance the positive electrode active material that ultimately does notcycle. In some embodiments, the irreversible capacity loss is no morethan about 60 mAh/g, in further embodiments no more than about 55 mAh/g,and in other embodiments from about 30 mAh/g to about 50 mAh/g. Withrespect to balancing of various battery parameters, the irreversiblecapacity loss can be between about 40 mAh/g to about 60 mAh/g.Similarly, in some embodiments, the irreversible capacity loss is notmore than about 19% and in further embodiments no more than about 18% ofthe first cycle specific charge capacity. A person of ordinary skill inthe art will recognize that additional ranges of irreversible capacityloss are contemplated and are within the present disclosure.

Average voltage may be an important parameter for batteries for certainapplications. The average voltage can relate to the available capacityabove a certain voltage. Therefore, in addition to having a highspecific capacity it is desirable for a positive electrode activematerial to also cycle with a high average voltage. For the materialsdescribed herein that are cycled between 4.6V and 2.0V, an averagevoltage can be at least about 3.475V, in further embodiments at leastabout 3.5V, in additional embodiments at least about 3.525V and in otherembodiments from about 3.55V to about 3.65V. A person of ordinary skillin the art will recognize that additional ranges of average voltagewithin the explicit ranges above are contemplates and are within thepresent disclosure.

In general, various similar testing procedures can be used to evaluatethe capacity performance of the battery positive electrode materials.Some specific testing procedures are described for the evaluation of theperformance values described herein. Suitable testing procedures aredescribed in more detail in the examples below. Specifically, thebattery can be cycled between 4.6 volts and 2.0 volts at roomtemperature, although other ranges can be used with correspondinglydifferent results. Also, the specific capacity is very dependent on thedischarge rate. Again, the notation C/x implies that the battery isdischarged at a rate to fully discharge the battery to the selectedvoltage minimum in x hours.

In some embodiments, the positive electrode active material has aspecific capacity during the tenth cycle at a discharge rate of C/3 ofat least about 245 milliamp hours per gram (mAh/g), in additionalembodiments at least about 250 mAh/g, and in further embodiments fromabout 255 mAh/g to about 265 mAh/g. Additionally, the 40^(th) cycledischarge capacity of the material is at least about 94%, and in furtherembodiments at least about 95% of the 7^(th) cycle discharge capacity,cycled at a discharge rate of C/3.

The maintenance of the specific capacity at 40 cycles relative to thespecific capacity at the 7th cycle can also be referred to as thecoulombic efficiency, as described further in the examples. Also, thecoated materials can exhibit surprisingly good rate capability.Specifically, the materials can have a specific discharge of at leastabout 190 mAh/g, in further embodiments at least about 195 mAh/g and inadditional embodiments at least about 200 mAh/g at a rate of 2 Cdischarged from 4.6V to 2.0V at room temperature at the 15thcharge/discharge cycle. A person of ordinary skill in the art willrecognize that additional ranges of specific capacity are contemplatedand are within the present disclosure.

In general, the results herein suggest a balance of factors that resultin particularly desirable battery performance for a thin coating overthe active material for the positive electrode. The results in theexample suggest that thicker coatings may result in a greater impedancethat may contribute to the capacity and voltage performances observed.With an appropriate thin coating, excellent specific capacities,coulombic efficiency and average voltages can be obtained.

EXAMPLES

The Examples include data obtained using coin cells as well asadditional data with cylindrical cells. The formation of the coin cellswith a lithium foil negative electrode is summarized in thisintroduction, and the formation of the coin cells with carbon basedelectrodes is described in Example 5 below. The coin cell batteriestested in Examples 1, 3 and 4 were produced following a procedureoutlined here. The lithium metal oxide (LMO) powders were mixedthoroughly with acetylene black (Super P™ from Timcal, Ltd, Switzerland)and graphite (KS 6™ from Timcal, Ltd) to form a homogeneous powdermixture. Separately, Polyvinylidene fluoride PVDF (KF1300™ from KurehaCorp., Japan) was mixed with N-methyl-pyrrolidone NMP(Honeywell-Riedel-de-Haen) and stirred overnight to form a PVDF-NMPsolution. The homogeneous powder mixture was then added to the PVDF-NMPsolution and mixed for about 2 hours to form a homogeneous slurry. Theslurry was applied onto an aluminum foil current collector to form athin wet film.

A positive electrode material was formed by drying the aluminum foilcurrent collector with the thin wet film in vacuum oven at 110° C. forabout two hours to remove NMP. The positive electrode material waspressed between rollers of a sheet mill to obtain a positive electrodewith desired thickness. An example of a positive electrode compositiondeveloped using above process having a LMO:acetylene black:graphite:PVDFratio of 80:5:5:10 is presented below.

The positive electrode was placed inside an argon filled glove box forthe fabrication of the coin cell batteries. Lithium foil (FMC Lithium)having thickness of 150 micron was used as a negative electrode. Theelectrolyte was a 1 M solution of LiPF₆ formed by dissolving LiPF6 saltin a mixture of ethylene carbonate, diethyl carbonate and dimethylcarbonate (from Ferro Corp., Ohio USA) at a 1:1:1 volumetric ratio. Atrilayer (polypropylene/polyethylene/polypropylene) micro-porousseparator (2320 from Celgard, LLC, NC, USA) soaked with electrolyte wasplaced between the positive electrode and the negative electrode. A fewadditional drops of electrolyte were added between the electrodes. Theelectrodes were then sealed inside a 2032 coin cell hardware (HohsenCorp., Japan) using a crimping process to form a coin cell battery. Theresulting coin cell batteries were tested with a Maccor cycle tester toobtain charge-discharge curve and cycling stability over a number ofcycles. All the electrochemical data contained herein have been cyclingat three rates, 0.1 C (C/10) for the first three cycles, 0.2 C (C/5) forcycles 4-6 or 0.33 C (C/3) for cycles 7 and on.

Example 1 Reaction of Metal Sulfate with Na₂CO₃/NH₄OH for CarbonateCo-Precipitation

This example demonstrates the formation of a desired cathode activematerial using a carbonate co-precipitation process. Stoichiometricamounts of metal sulfates (NiSO₄.xH₂O, CoSO₄.xH₂O, & MnSO₄.xH₂O) weredissolved in distilled water to form a metal sulfate aqueous solution.Separately, an aqueous solution containing Na₂CO₃ and NH₄OH wasprepared. For the formation of the samples, the two solutions weregradually added to a reaction vessel to form metal carbonateprecipitates. The reaction mixture was stirred, and the temperature ofthe reaction mixture was kept at a temperature between room temperatureand 80° C. for 2-24 hours. The pH of the reaction mixture was in therange from 6-9. In general, the aqueous metal sulfate solution had aconcentration from 1M to 3M, and the aqueous Na₂CO₃/NH₄OH solution had aNa₂CO₃ concentration of 1M to 4M and a NH₄OH concentration of 0.2-2M.The metal carbonate precipitate was filtered, washed multiple times withdistilled water, and dried at 110° C. for about 16 hrs to form a metalcarbonate powder. Specific ranges of reaction conditions for thepreparation of the samples are further outlined in Table 1.

TABLE 1 Reaction Process Condition Values Reaction pH 6.0-9.0 Reactiontime 2-24 hr Reactor type Batch Reactor agitation speed 200-1400 rpmReaction temperature RT-80° C. Concentration of the metal salts 1-3MConcentration of Na₂CO₃ (precipitating agent) 1-4M Concentration ofNH₄OH (chelating agent) 0.2-2M   Flow rate of the metal salts 1-100mL/min Flow rate of Na₂CO₃ & NH₄OH 1-100 mL/min

An appropriate amount of Li₂ CO₃ powder was combined with the driedmetal carbonate powder and thoroughly mixed by a Jar Mill, doubleplanetary mixer, or dry powder rotary mixer to form a homogenous powdermixture. A portion, e.g. 5 grams, of the homogenized powders is calcinedfollowed by an additional mixing step to further homogenize the powderformed. The further homogenized powder was again calcined to form thelithium composite oxide. The product composition was determined to beLi_(1.2)Ni_(0.175)Co_(0.10)Mn_(0.525)O₂. Specific ranges of calcinationconditions are further outlined in Table 2.

TABLE 2 Calcination Process Condition Values 1^(st) Step temperature400-800° C. time 1-24 hr protective gas Nitrogen or Air Flow rate ofprotective gas 0-50 scfh 2^(nd) Step temperature 700-1100° C. time 1-36hr protective gas Nitrogen or Air Flow rate of protective gas 0-50 scfh

Scanning electron microscope (SEM) micrograms at differentmagnifications of the lithium composite oxides are shown in FIG. 2A andFIG. 2B, indicating the particles formed have a substantially sphericalshape and are relatively homogenous in size. The x-ray diffractionpattern of the pristine composite powder is shown in FIG. 3, showingcharacteristics of a rock-salt type structure.

The composite was used to form a coin cell battery following theprocedure outlined above. The coin cell battery was tested and the plotof voltage versus specific capacity at discharge rate of 0.1 C for thefirst cycle and 0.33 C for the 7th cycle are shown in FIGS. 4A & 4B,respectively. The first cycle specific capacity of the battery at 0.1 Cdischarge rate is about 245 mAh/g. The 7th cycle specific capacity ofthe battery at 0.33 C discharge rate is about 220 mAh/g. Specificcapacity versus cycle life of the coin cell battery is also tested andthe results are shown in FIG. 5. The first three cycles were measured ata discharge rate of 0.1 C. The next three cycles were measured at a rateof 0.2 C. The subsequent cycles were measured at a rate of 0.33 C. Thebattery maintained more than 90% specific capacity relative to cycle 7after going through 40 charge and discharge cycles.

Example 2 Formation of AlF₃ Coated Metal Oxide Materials

The metal oxide particles prepared in the above example were coated witha thin layer of aluminum fluoride (AlF₃) using a solution-based method.For a selected amount of aluminum fluoride coating, an appropriateamount of saturated solution of aluminum nitrate was prepared in anaqueous solvent. The metal oxide particles were then added into thealuminum nitrate solution to form a mixture. The mixture was mixedvigorously for a period of time to homogenize. The length of mixingdepends on the volume of the mixture. After homogenization, astoichiometric amount of ammonium fluoride was added to the homogenizedmixture to form aluminum fluoride precipitate while retaining the sourceof fluorine. Upon the completion of the precipitation, the mixture wasstirred at 80° C. for 5 h. The mixture was then filtered and the solidobtained was washed repeatedly to remove any un-reacted materials. Thesolid was calcined in nitrogen atmosphere at 400° C. for 5 h to form theAlF₃ coated metal oxide material. SEM micrograms at differentmagnifications of representative AlF₃ coated lithium composite oxide areshown in FIG. 2C and FIG. 2D, indicating the particles formed have asubstantially spherical shape and are relatively homogenous in size.

Samples of lithium metal oxide (LMO) particles synthesized as describedin example 1 were coated with various selected amounts of aluminumfluoride using the process described in this example. Transmissionelectron microscopy was used to assess the thickness of the resultingAlF₃ coatings. For instance, FIG. 6A shows a transmission electronmicrograph (TEM) of an uncoated lithium composite oxide particle, FIG.6B shows a TEM micrograph of a LMO particle with an approximately 7 nmthick AlF₃ coating, and FIG. 6C shows a TEM micrograph of a LMO particlewith an approximately 25 nm AlF₃ coating. The coatings wereapproximately constant thickness over the particle surfaces. The x-raydiffraction pattern of the aluminum fluoride coated LMO samples withcoating thickness of 3 nm, 6 nm, 11 nm, 22 nm, and 40 nm are shown inFIG. 3 along with the diffractogram for the pristine, i.e., uncoated,sample. All of the x-ray diffractograms exhibit characteristics of arock-salt type structure as the uncoated LMO sample. The aluminumfluoride coated LMOs were then used to form coin cell batteriesfollowing the procedure outlined above. The coin cell batteries weretested as described in the following Example.

The stability of the cathode active materials was studied usingdifferential scanning calorimetry (DSC). The DSC results are shown inFIG. 7 for uncoated LMO particles and particles with 4 different coatingthicknesses. Peaks in the heat flow as a function of temperatureindicate a phase transition or similar change of the material. From FIG.4, it can be seen that all of the coating thicknesses stabilize thematerial relative to the low temperature active phase, although greatercoating thicknesses further increased the stability. Therefore, it isexpected that batteries formed with the materials should exhibit greatertemperature stability at higher temperatures if coated LMO materials areused in the positive electrodes.

Example 3 Battery Performance for AlF₃ Coated Samples

This example demonstrates how the battery performance varied withrespect to coating thickness for a range of AlF₃ coating thicknesses andfor various battery performance parameters.

The impedance of the positive electrodes was examined usingelectrochemical impedance spectroscopy (EIS). This data providesinformation on the interfacial characteristics of the coated materials.The electrode is perturbed with a current in the form of a sinusoidalwave. A plot of the EIS results is presented in FIG. 8. These resultsshow that a greater charge transfer resistance results form thicker AlF₃coatings.

Coin cell batteries were formed from the materials synthesized asdescribed in Example 2 using the process and coin cell structuredescribed above. The cells were cycled to evaluate their performance.The first three cycles were measured at a charge/discharge rate of 0.1C. The next three cycles were measured at a charge/discharge rate of 0.2C. The subsequent cycles were measured at a charge/discharge rate of0.33 C.

Plots of voltage versus specific capacity of the coin cell batteryformed from 3 nm aluminum fluoride coated LMO material are shown in FIG.9A for the first cycle at a charge/discharge rate of 0.1 C and FIG. 9Bfor the 7th cycle at a charge/discharge rate of 0.33 C. The first cyclespecific capacity of the battery at 0.1 C discharge rate was about 265mAh/g. The first cycle specific capacity of the battery at 0.33 Cdischarge rate is about 250 mAh/g. Specific capacity versus cycle of thecoin cell battery was also tested and the results are shown in FIG. 10.The positive electrode active material of the battery maintained morethan 95% of its specific capacity relative to the specific capacity atcycle 7, the first C/3 cycle, after going through 40 charge anddischarge cycles.

Plots of voltage versus specific capacity of the coin cell batteryformed from 22 nm aluminum fluoride coated LMO material and 0.33 areshown in FIG. 11A for the 1st cycle at discharge rate of 0.1 C and FIG.11B for the 7th cycle at a discharge rate of C/3. The first cyclespecific capacity of the battery at 0.1 C discharge rate was about 260mAh/g. The 7th cycle specific capacity of the battery at 0.33 Cdischarge rate was about 235 mAh/g. Specific capacity versus cycle ofthe coin cell battery was also tested and the results are shown in FIG.12. The battery maintained approximately 98% specific capacity aftergoing through 40 charge and discharge cycles relative to the 7th cyclespecific capacity.

Specific capacity versus cycle of the coin cell batteries formed fromuncoated, 3 nm, 6 nm, 11 nm, 22 nm, and 40 nm aluminum fluoride coatedLMO materials were tested and the results are shown in FIG. 13.Batteries with the coated LMO materials showed a complex relationshipbetween specific capacity performance as a function of the coatingthickness. Batteries with LMO materials having a 6 nm aluminum fluoridecoating had the highest specific capacity at low cycle number, whilebatteries with LMO materials having a 4 nm aluminum fluoride coating hadthe highest capacity at 40 cycles. Battery with LMO materials having 40nm coating had the lowest specific capacity, which was lower than thebattery with the uncoated material, but this battery exhibited a slightincrease in capacity with cycling.

The first cycle irreversible capacity loss (IRCL) of the batterieshaving uncoated, 3 nm, 6 nm, 11 nm, 22 nm, and 40 nm aluminum fluoridecoated LMO materials were measured. A plot of the results in percentageof overall capacity versus coating thickness is shown in FIG. 14A, and aplot of the results in specific capacity change as a function of coatingthickness is shown in FIG. 14B. The IRCL results showed a steadydecrease of the IRCL for batteries with coating thicknesses to about 10nm, and the IRCL roughly leveled off with for batteries having 11 nm, 22nm, and 40 nm aluminum fluoride coated LMO materials.

The average voltages of the batteries were measured for batteries havingpositive electrodes with uncoated, 3 nm, 6 nm, 11 nm, 22 nm, and 40 nmaluminum fluoride coated LMO materials. The average voltage was takenover a discharge from 4.6V to 2.0V. A plot of average voltage as afunction of coating thickness is shown in FIG. 15A, and a plot ofpercentage of voltage reduction relative to the uncoated materialperformance versus coating thickness is shown in FIG. 15B. The averagevoltage generally showed a decrease versus increased aluminum fluoridecoating thickness on the LMO materials, although the decrease in averagevoltage was small for coatings of 6 nm or less.

Additionally, the coulombic efficiency of the batteries having uncoated,3 nm, 6 nm, 11 nm, 22 nm, and 40 nm aluminum fluoride coated LMOmaterials were measured. As used here, the coulombic efficiency isevaluated as the specific capacity at cycle 40 as a percentage of thespecific capacity at cycle 7, the first cycle at a rate of C/3. In otherwords, the coulombic efficiency is 100×(specific capacity at cycle40)/(specific capacity at cycle 7). A plot of the coulombic efficiencyas a function of coating thickness is shown in FIG. 16. The coulombicefficiency increased by about 2% when coating thickness is increasedfrom zero to 3 nm. The coulombic efficiency then decreased significantlywhen coating thickness is increased from 3 nm to 6 nm and 11 nm. Thecoulombic efficiency increased dramatically for batteries formed withpositive electrode active materials when the coating thickness was 22 nmand 40 nm.

Example 4 Materials with Metal Bifluoride Coatings and CorrespondingBatteries

This example described the formation of coating of MgF₂, CaF₂, BaF₂ andSrF₂ on the lithium rich metal oxides, and corresponding coil cell datais presented indicating the improved performance for the coatedmaterials.

Samples of lithium metal oxide (LMO) particles synthesized as describedin Example 1 were coated with 1-4 nm of MgF₂, CaF₂, BaF₂ and SrF₂. Astoichiometric amount of the selected metal nitrate, such as magnesiumnitrate, was dissolved in water and mixed with the corresponding amountof the lithium metal oxide under constant stirring. Then, ammoniumfluoride was added to the mixture slowly while continuing the stirring.After the addition of an excess of ammonium fluoride, the mixture washeated to about 80° C. for about 5 hours. After the deposition wascompleted, the mixture was filters and calcined at 450° C. for 5 hoursunder a nitrogen atmosphere. The x-ray diffraction pattern of the metalbifluoride coated LMO samples in FIG. 17 along with the diffractogramfor the corresponding pristine, i.e., uncoated, sample. All of the x-raydiffractograms exhibit characteristics of a rock-salt type structure asthe uncoated LMO sample. Transmission electron micrographs are shown inFIGS. 18A and 18B for MgF₂ (A) coated samples and SrF₂ (B) coatedsamples.

The metal bifluoride coated LMOs were used to form coin cell batteriesfollowing the procedure outlined above. A plot of the voltage from 4.6 Vto 2.0 V versus specific charge and discharge capacity is shown in FIG.19 for the first cycle for the uncoated material at a rate of C/10. Thisbatch of LMO material had a slightly greater specific capacity comparedwith the uncoated material used to obtain FIG. 4a . Corresponding plotsof voltage versus specific charge and discharge capacities are presentedin FIGS. 20-23 for MgF₂, SrF₂, BaF₂ and CaF₂, respectively, at a rate ofC/10. These four first cycle plots for batteries with positiveelectroactive materials having different metal bifluoride coatingsexhibited similar first cycle performance with the materials having anMgF₂ coating exhibiting a somewhat higher discharge specific capacity.These cells were cycled for 16 cycles with a rate of C/10 for cycles 1and 2, C/5 for cycles 3 and 4, C/3 for cycles 5 and 6, 1 C for cycles7-11 and 2 C for cycles 12-16. The cycling results are presented in FIG.24. All of the batteries prepared with coated samples exhibitedsignificantly greater discharge specific capacity at all rates relativeto a battery formed with the uncoated composition. The batteries formedwith materials having a coating of

SrF₂, BaF₂ and CaF2 exhibited similar performance while the batteryformed with the positive electroactive material coated with MgF2exhibited somewhat greater specific discharge capacity at all rates.

Example 5 Coin Cells Formed With AlF₃ Coated Compositions

The Example explores the battery performance for coin cell batteriesusing graphite as the negative electrode active materials.

Lithium metal oxide (LMO) powders produced as described in Example 1were mixed thoroughly with conductive carbons, such as a mixtureacetylene black and graphite, to form a homogeneous powder mixturecomprising from 10-20 weight percent conductive carbon. Separately,polyvinylidene fluoride (PVDF) was mixed with N-methyl-pyrrolidone (NMP)and stirred overnight to form a PVDF-NMP solution. The homogeneouspowder mixture was then added to the PVDF-NMP solution and mixed for 2-6hours to form homogeneous slurry. The slurry was applied onto analuminum foil current collector to form a thin wet film using acommercial coater.

A positive electrode structure was formed by drying the aluminum foilcurrent collector with the thin wet film electrode to remove NMP. Thepositive electrode and current collector were pressed together betweenrollers of a sheet mill to obtain a positive electrode with desiredthickness in association with the foil current collector.

A blend of graphite, optional conductive carbon and binder was used asthe negative electrode to have from about 80-99 weight percent graphite.The negative electrode composition was coated onto a copper foil currentcollector and dried. A trilayer(polypropylene/polyethylene/polypropylene) micro-porous separator (2320from Celgard, LLC, NC, USA) soaked with electrolyte was placed betweenthe positive electrode and the negative electrode. A few additionaldrops of electrolyte were added between the electrodes. The electrodestack with the positive electrode-separator-negative electrode wasplaced within coin cells. The electrolyte was a 1 M solution of LiPF6form by dissolving LiPF6 salt in a mixture of ethylene carbonate,diethyl carbonate and dimethyl carbonate (from Ferro Corp., Ohio USA) ata 1:1:1 volumetric ratio. The electrolyte was placed in the cell withthe electrode stack and the coin cell was sealed.

The resulting batteries were tested with a Maccor cycle tester to obtaincharge-discharge curve and cycling stability over a number of cycles.The first cycle was performed at a rate of C/10, and cycles 2-50 wereperformed at a rate of C/3. The results for the uncoated, i.e.,pristine, sample and samples with 5 different AlF₃ coating thicknessesare plotted in FIG. 25 in terms of specific capacity as a function ofcycle. The batteries formed with an AlF₃ coating having a thickness of 3nm showed significantly greater specific capacities after the first fewcycles.

Example 6 Alternative Positive Electroactive Composition With AlF₃Coatings and Corresponding Batteries

This example demonstrates battery performance results with analternative electroactive material for the positive electrode having aselected amount of AlF₃ coating composition.

The positive electrode active material was synthesized as described inExample 1. However, the product composition used for the positiveelectrodes of the batteries in this example wasLi_(1.07)Ni_(0.31)Co_(0.31)Mn_(0.31)O₂. Particles of the productcomposition were coated with AlF₃ as described in Example 2. Sampleswere prepared with different amounts of AlF₃ coating compositions.Representative transmission electron micrographs are given in FIGS. 26Aand 26B showing average coating thicknesses of about 3 nm (A) and about17 nm (B).

Coin cell batteries were formed using the process and coin cellstructure described above. The cells were cycled to evaluate theirperformance. The first two cycles were measured at a charge/dischargerate of 0.1 C. The subsequent cycles 3-18 were measured at acharge/discharge rate of 0.33 C. One set of samples were cycled between2.0V and 4.3 V while a second set of samples were cycled from 2.0V to4.5V.

The voltage as a function of specific capacity is plotted in FIGS. 27and 28 for an uncoated positive electrode active material and a positiveelectrode active material with uncoated active material (FIG. 27) orabout 3 nm thickness AlF₃ coating (FIG. 28) for cycling between 2.0V and4.3V. The battery formed with the coated sample exhibited a greaterdischarge capacity and a corresponding reduction in irreversiblecapacity loss. Similar results were found with cycling between 2.0V and4.5V. The plots of voltage as a function of specific capacity forcycling between 2.0V and 4.45V are presented in FIGS. 29 and 30,respectively, for positive electrode active materials that are uncoated(FIG. 29) or with a approximately 3 nm AlF₃ coating (FIG. 30). Asexpected, the charge and discharge capacities are greater for thecycling to a higher voltage.

Specific capacity versus cycle of the coin cell batteries formed fromuncoated, 3 nm, 8 nm, 17 nm, 22 nm, and 47 nm aluminum fluoride coatedLMO materials were tested for cycling between 2.0V and 4.3V as well as2.0V to 4.5V. The specific discharge capacity as a function of cycle forcycling between 2.0V and 4.3V are shown in FIG. 31, and the specificdischarge capacity as a function of cycle for cycling between 2.0V and4.5V are shown in FIG. 32. Batteries with the present coated LMOmaterials showed a specific capacity performance that decreased withincreasing coating thickness, although some materials with differentcoating thicknesses had essentially identical specific capacity results,as seen in FIGS. 31 and 32. The material with the thickest coatingconsistently had lower specific capacity than the uncoated materials,while the remaining coated materials exhibited a greater specificcapacity relative to the uncoated materials. These results arequalitatively consistent with the result in FIGS. 13 and 25 in whichthick coating have a lower specific capacity than uncoated samples andthin coatings achieve the best specific capacity performance uponcycling.

The embodiments above are intended to be illustrative and not limiting.Additional embodiments are within the claims. In addition, although thepresent invention has been described with reference to particularembodiments, those skilled in the art will recognize that changes can bemade in form and detail without departing from the spirit and scope ofthe invention. Any incorporation by reference of documents above islimited such that no subject matter is incorporated that is contrary tothe explicit disclosure herein.

What is claimed is:
 1. A lithium ion battery comprising a positiveelectrode, a negative electrode comprising a lithium incorporationcomposition, a separator between the positive electrode and the negativeelectrode and an electrolyte comprising lithium ions, wherein thepositive electrode comprises an active material, distinct electricallyconductive powders and a polymer binder, wherein the positive electrodeactive material comprises an active lithium metal oxide compositioncoated with an inorganic coating composition, and the positive electrodeactive material having a discharge specific capacity of at least about190 mAh/g with a discharge rate of 2 C from 4.6 volts to 2.0 volts atroom temperature for the fifteenth charge/discharge cycle.
 2. Thelithium ion battery of claim 1 wherein the negative electrode comprisesgraphitic carbon.
 3. The lithium ion battery of claim 1 wherein theinert inorganic coating composition comprises a metal/metalloidfluoride.
 4. The lithium ion battery of claim 1 wherein the coatingcomposition has an average thickness from about 0.5 nm to about 12 nm.5. The lithium ion battery of claim 1 wherein the inert inorganiccoating composition comprises a metal/metalloid oxide.
 6. The lithiumion battery of claim 1 wherein the active lithium metal oxidecomposition is approximately represented by the formulaLi_(1+x)M_(1+x)O₂, where M is a metal element or a combination thereofand 0.01≦x≦0.3.
 7. The lithium ion battery of claim 1 wherein the activelithium metal oxide composition can be approximately represented by aformula of bLiM′O₂.(1−b) Li₂M″O₃, where M′ represents one or more metalions having an average valance of +3 and M″ represents one or more metalions having an average valance of +4 and 0<b<1.
 8. The lithium ionbattery of claim 1 wherein the active lithium metal oxide compositioncan be approximately represented by a formulaLi_(1+x)Ni_(α)Mn_(β)Co_(γ)A_(δ)O₂, where x ranges from about 0.05 toabout 0.25, α ranges from about 0.1 to about 0.4, β ranges from about0.4 to about 0.65, γ ranges from 0 to about 0.3, and δ ranges from 0 toabout 0.1, and where A is Mg, Zn, Al, Ga, B, Zr, Ti, Ca, Ce, Y, Nb, Cr,Fe, V, Li or combinations thereof.
 9. The lithium ion battery of claim 1wherein the irreversible capacity loss of the battery is reduced by atleast about 10% relative to the irreversible capacity loss of anequivalent battery formed with the uncoated active lithium metal oxide.10. The lithium ion battery of claim 1 wherein the active lithium metaloxide composition has a tap density of at least about 1.3 g/mL.
 11. Alithium ion battery comprising a positive electrode, a negativeelectrode comprising a lithium incorporation composition and a separatorbetween the positive electrode and the negative electrode, wherein thepositive electrode comprises an active material having an active lithiummetal oxide composition coated with an inorganic coating composition,distinct electrically conductive powers and a polymer binder, thepositive electrode active material having a discharge specific capacityof at least about 245 mAh/g, an average voltage of at least about 3.55volts and a capacity at 40 cycles that is at least about 90% of thecapacity at 10 cycles with a discharge rate of C/3 from 4.6 volts to 2.0volts at room temperature.
 12. The lithium ion battery of claim 11wherein the positive electrode active material has a specific capacityof at least about 250 mAh/g with a discharge rate of C/3 from 4.6 voltsto 2.0 volts at room temperature.
 13. The lithium ion battery of claim11 wherein a capacity at 40 cycles that is at least about 95% of thecapacity at 10 cycles with a discharge rate of C/3 from 4.6 volts to 2.0volts at room temperature.
 14. The lithium ion battery of claim 11wherein the inorganic coating composition comprises a metal/metalloidfluoride.
 15. The lithium ion battery of claim 11 wherein the inorganiccoating composition comprises AlF₃, MgF₂, CaF₂, SrF₂ or BaF₂.
 16. Thelithium ion battery of claim 11 wherein the inorganic coating has anaverage thickness from about 1 nm to about 8 nm.
 17. The lithium ionbattery of claim 11 wherein the active lithium metal oxide compositioncan be approximately represented by the formula Li_(1+x)M_(1−x)O₂, whereM is one or more metal elements and 0.01≦x≦0.3.
 18. The lithium ionbattery of claim 11 wherein the active lithium metal oxide compositioncan be approximately represented by a formula of bLiM′O₂.(1−b) Li₂M″O₃,where M′ represents one or more metal ions having an average valance of+3 and M″ represents one or more metal ions having an average valance of+4 and 0<b<1.
 19. The lithium ion battery of claim 11 wherein the activelithium metal oxide composition can be approximately represented by aformula Li_(1+x)Ni_(α)Mn_(β)Co_(γ)M″_(δ)O₂, where x ranges from about0.05 to about 0.25, α ranges from about 0.1 to about 0.4, β ranges fromabout 0.4 to about 0.65, γ ranges from 0 to about 0.3, and δ ranges from0 to about 0.1, and where M″ is Mg, Zn, Al, Ga, B, Zr, Ti, Ca, Ce, Y,Nb, Cr, Fe, V, Li or combinations thereof.
 20. The lithium ion batteryof claim 11 wherein the negative electrode comprises graphitic carbon.